Best way to store hydrogen

doi:10.1038/nindia.2011.13 Published online 31 January 2011

Researchers have successfully revealed the hydrogen storage capacity of clathrate hydrates, crystalline water-based solids physically resembling ice. The ability of clathrate hydrates to store hydrogen is important because it is an extremely environmentally friendly fuel.

Burning fossil fuels such as oil, natural gas and coal releases gases that contribute to global warming. Hydrogen is a clean, highly abundant and nontoxic renewable fuel. However, the major problem with hydrogen is that it must be stored like other compressed gases.

Clathrate hydrates can incorporate guest molecules inside the polyhedral cages of their host framework, and have therefore generated much interest as a potential hydrogen storage material. The researchers performed computer-based simulation studies to explore the potential of clathrate hydrates to store hydrogen molecules.

Clathrate hydrates generally form two cubic structures — type I and type II — but may sometimes form a third hexagonal cubic structure known as type H, which consists of cages of water molecules. Type H clathrate hydrates function as host complexes, in which the host molecules are water and the guest molecules are gases.

Computational studies reveal that clathrate hydrate cage structures may accommodate between two and six hydrogen molecules, and that hydrogen molecules would prefer to be trapped inside the cavity rather than outside.

The study also indicates that increasing the number of hydrogen molecules in the cage enhances the stability of clathrate hydrates in most cases. Both thermodynamic and kinetic data suggest that clathrate hydrates have potential to be used as a good hydrogen storage material, the researchers say.